System for attaining uniform attenuation



May 1, 1923. 1,454,021

0. B. BLACKWELL SYSTEM FOR ATTAINING UNIFORM ATTENUATION Filed June 29, 1918 3 Sheets-Sheet 1 IN VEN TOR.

ATTORNEY",

May 1, 1923. r 1,454,011

0. B. BLACKWELL SYSTEM FOR ATTAINING UNIFORM ATTENUATION Filed June 29, 1918 3 Sheets-Sheet 2 May 1 1923. 1,454,011

O. B. BLACKWELL SYSTEM FOR ATTAINING UNIFORM ATTENUATION Filed June 29, 1918 3 Sheets-Sheet 3 Nassau and State of ill,

OTTO B. BLACKWELL, OF GARDEN CITY, NEW YORK, PHONE AND TELEGRAPH COM?ANY A CORPORATION 01* SYSTEM FOR ATTAININQ UNIFO Application filed June 29,

To all whom it may concern:

Be it known that 1-; O'r'ro B. BLACKWELL, residing at Garden Ciiy, in the county of ew York, have invented certain Improvements in Systems for Attaining Uniform Attenuation, of which the following is a specification.

This invention relates to transmission systems and more particularly to transmission systems over which telephonic or multifrequency signals are transmitted.

In a system used for the transmission of frequencies varying over a considerable range, the attenuation varies for different frequencies, and in the case of telephonic signals. the higher frequencies are usually attenuated to such an extent as compared with the lowerfrequencies that a considerable degree of distort-ion results, and this is true even where the transmission line is loaded. It is possible, however, to design an auxiliary system, such as a network, so that the lower frequencies are attenuated to agreater degree than the higher frequencies. v

associating such an auxiliary system with the transmission system proper, the attenuation as regards the combination may be made substantially the same for all frequencies Within a desired range. By proper design of the auxiliary system or network it is possible, when uniform transmission is not desired, to cause the attenuation of the combined system to vary with frequency in -any desired manner.

Such an arrangement is unsatisfactory, however, for the reason that the introduction of an auxiliary system into the trans; mission line for the purpose of equaliz'ingf; the attenuation increases the transmission loss of the system as a whole. Furthermore, the impedance of such an auxiliary system ordinarily varies with the frequency inv a manner differing radically from that of the transmission line. The introduction of the auxiliary system into the transmission line consequently results in irregularities which may produce reflection losses over and above the transmission losses due to the auxiliary system itself.

It is one of the objects of this invention to overcome the losses due to the introduction of the auxiliary system, by so associating the auxiliary system with the transmission line and an amplifying arrangement,

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that the amplifying arrangement will make up the losses due to the auxiliary system.

Another ob]ect of the invention is to reduce and 111' some instances substantially eliminate the above-mentioned reflection lossesdue to the auxiliary system by so associating the auxiliary system with the amplifyingarrangement that the reaction of the varying impedance of the auxiliary system upon the transmission line is prevented either in whole or part.

'lhese objects as well as other objects wh ch will be clear from the detailed description of the invention are accomplished by introducing into the transmission line a repeater arrangement, preferably of the two-way two-repeater type, or of the socalled four-wire type,iand by introducing the auxiliary system into some element of the repeater circuit, preferably in the local branches including the repeater elements in the case of the two-way two-repeater arrangement and in the pair of one-way lines interconnecting two stations in the'case of the four-wire circuit. a By this location of the auxiliary system it will be rendered electricall more remote from the transmissionjline t an it itwere directly included therein, so that its variable impedanceproduces less reaction upon the line. Where two-stage amplifiers are used in the repeater circuits, by locating the auxiliary system between two amplifying elements, its reaction-upon the line may be eliminated, as the amplifying elements are one-we devices.

The invention may now be more fully understood from the following description,

when read in connection with the accomassociated with the repeater circuit through transformers 1 and 1', andare balanced with 10@ or attenuation equalizer in a four-wire rerespect to repeater circuits by means of artificial lines or networks N, and N transformers 2 and 2' being associated with the artificial lines for the purpose of balancing the transformers 1 and 1'. The usual three winding transformers T, and T are provided, the input circuit of the amplifier A,

being associated with the bridge across the mid-points of the windin s of the transformer T,, through a trans ormer 3, the output circuit of the amplifier including the third winding of the transformer T In a similar manner the input circuit of the amplifier A, is associated with the bridge across the windings of the transformer T by Thus the amplifiers A, and A which are shown as being of the well known vacuum tube type may be of any other well known type such as the so-called mechanical repeater. In order to equalize the attenuation due to the characteristics of the transmission lines L, and L and other factors (such, for instance, as terminal reflection efi'ects) or to cause the attenuation to vary with frequency. in any desired manner, auxiliary systems or attenuation equalizers E, and E E, and E, are provided. These attenuation equalizers, as illustrated, are of the series impedance ty e disclosed in a copending application of ay S. Hoyt, Serial No. 242,567, filed June 29, 1918, and the theory of the operation of this type of equalizer is fully set forth in said application. In so far as the purposes of this invention are concerned, however, any of the other types of attenuation equalizers disclosed in the said application may he used in place of the series impedance type or in fact any other well known type of equalizer may be employed, provided it is associated with the transmission line and the repeater arrangement in such manner as to secure the objects sought by this invention.

Certain of the desired results may be obtained by locating the attenuation equalizer between the two halves of one of the windings of the transformers l and 1 associating the transmission lines with the repeater circuit. Thus the equalizer E, is associated with the right-hand winding of the transformer E, and the equalizer E, is associated with the lefthand winding of the transformer 1'. In order to balance these equalizers with respect to the repeater equalizers E and E, are similarly connected to the transformers 2 and 2' upon the artificial Leeann 1 line side. By means of this arrangement the attenuation equalizers, when taken in connection with the transmission lines, constitute circuits in which all frequencies Within a definite range are transmitted with approximately the same attenuation, the equalizer being proportioned with regard to the electrical characteristics of the line and the frequencies transmitted to secure this result as described in the above mentioned application of Ray S. Hoyt. The losses due to the. attenuation equalizer are overcome by means of the gain in transmission introduced by the repeater; andby providing the attenuation equalizers in pairs upon the line and artificial line side of the repeater, singing may be avoided. The arrangement shown in Fig. 1, however, may introduce some difiiculty because of the fact that ordinarily its impedance varies with the frequency in a manner different from that of the transmission line, so that irregularities may result which may produce reflection losses over and above the transmission losses due to the equalizer itself.

While this difiiculty is not of sufficient importance to inhibit the use of the arrangement shown in Fig. 1, it may to a considerable extent be eliminated by the arrangement shown in Fig. 2 in which, instead of associating the equalizers directly with the line through a transformer, the equalizers are included in the input brid es of the repeater. Thus the equalizer 3 is inserted between the two halves of the primary winding of transformer 3, while the equalizer E, is inserted in the rimary winding. of the transformer 3'. hile in this arrangement the impedance of the attenuation equalizer ordinarily varies with the frequency as before, it is electrically more distant from the transmission line than in the arrangement of Fig. 1. This arrangement has a further advantage over that of Fig. 1 that only two attenuation equalizers are required due to the fact that the equalizer is not included in a balanced part of the circuit.

Substantially the same results may be obtained by means of the arrangement shown in Fig. 3, in which the attenuation equalizers are included in the output circuits of the amplifiers A, and A, respectively. Thus the attenuation equalizer E, is inserted between the two halves of the third winding of the transformer T while the equalizer E, is inserted between the two halves of the third windin of the transformer T,. Here again, as in Fig. 2, the variable impedance of the attenuation equalizer produces a relatively smaller efiect upon the total impedance of the repeater as seen from the line.

The edect of the variable impedance of the attenuation equalizer upon the total impedance of the repeater circuit, as seen from X In the line, may be eliminated by employing the arrangement shown in Fig. 4. In this fi re, two-stage amplifiers are employed. T us for transmission from line L to line L, two amplifiers A and A, are employed, while for transmission from-L to L amplifiers A and A are emplolyed. By inserting the attenuation equalizer 4 between the amplifiers A, \and A and the exlalizer E between the amplifiers A and the efiect of the variable impedance of the equalizer upon the impedance as viewed from the line is eliminated, due to the fact that the amplifiers are one-way devices. The arrangement shown in Fig. 4, while preferable in this re spect to the other three circuit arrangements, might be disadvantageous in an installation where two stage amplifiers are unnecessary in order to secure the desired transmission gain.

The above described arrangements, while in many respects e uivalent, are in fact electrically slightly difierent but any one of these arrangements permits of the use of an attenuation equalizer in a transmission systemwithout reducing the transmission of the system as a whole. It will be understood moreover that various combinations of the above described arrangementsof the attenuation equalizers may be employed, if desired.

Similar arrangements of the attenuation equalizers, w1th respect to the line and repeater arrangement, may be employed in connection with a four-wire circuit, as shown in Figs. 5 to 10, inclusive. A typical form of four-wire circuit is illustrated in Fig. 5 in which lines L and L terminating at two distant stations are interconnected through a four-wire circuit, including line sections L and L for transmission in one direction and line sections L and L for transmission in the opposite direction. Two-stage amplifiers A and A are inserted between the line sections L and L at an intermediate station and amplifiers A and A are inserted between the line sections L and L at said intermediate station. It will be. understood, however. that this arrangement is symbolical of a large number of possible arrangements, since single-stage amplifiers might be used, or, if desired, additional amplifiers might be inserted in the four-wire lines at other intermediate points. The four-wire circuit is associated with the terminating two-wire lines through the usual three-windingtransformers T and T and the transformers 1 and 1'. Lines 7 L and L are balanced by artificial lines N and N associated with which are transformers 2 and 2' for balancing the transformers 1 and 1'. The line section L is associated. with the input circuit of the amplifier by a transformer 3 and with the input connection from the line L, by means of a transformer 6.

' The line section L is associated with the output circuit of the amplifier A by means of a transformer 5 and with the output connection to the line L by means of a. transformer 7. In a similar manner line sections L, and L are associated with corresponding elements by means of transformers 3, 6' and 5', 7 respectively. As shown in Fig. 5, the attenuation equalizers E and E, are inserted between the two halves of one of the windings1 of the transformers 1 and 1 respective and are similarly connected to the transformers 2 and 2' on the artificial line side. This arrangement of the attenuation equal izers issubstantially the same as that shown in Fig. 1, the only difference being that the arrangement is shown as applied to a fourwire circuit insteadof a two-way two-repeater system.

Attenuation equalizers may be used to great advantage in connection with the four-wire system, due to the fact that in such a system losses may be inserted in each side of the four-wire circuit without limiting the transmission of the system, since any loss introduced may be made up by the introduction of a corresponding amplification without any resulting increased tendency to singing. Such a system, therefore,

admits of considerable latitude so far as the location of the attenuation equalizers is concerned, slnce any losses due to the locawhile the attenuation equalizers E tion of the equalizer in the four-wire link may be made up by means of the amplifiers in the circuit. This possibility is taken advantage of by the arrangements shown in Figs. 6 to 10, inclusive. Thus in Fig. 6 the attenuation equalizer E is inserted between the two halves of the primary winding of the transformer 6, associating the line section L with the input connection to the line L,. In a similar manner the attenuation equalizer E is connected with the transformer 6' in the path used for transmimion in the opposite direction. This arrangement is somewhat similar to that disclosed in Fig. 2 and has the same advantages.

In Fig. 7 the equalizer E is inserted between the two halves ofthe secondary winding of the transformer 3 in the input circuit of the amplifier A -The attenuation equalizer E is similarly associated with the transformer 3' in the other half of the four-wire link. This arrangement is slightly better than that of Fig. 6, since the attenuation equalizer iselectrically farther away from the terminatlng two-wire line sothat the variation in the impedance of the equalizer produces a correspondingly smaller efin the half of the four-wire link, while the attenuation e ualizer E, is inserted 'between the amp ifiers A, and A, in the other half. By means of this arrangement a line section of the four-wire link and the oneway amplifier separates the attenuation equalizer from the terminating two-wire line, so that the variable impedance of the former produces no effect upon the latter.

In Fig. 9 an arrangement is shown having substantially the same advantages as that shown in ig. 7. In accordance with this circuit arrangement the attenuation equalizer E is inserted between the two halves of the primary winding of the transformer 5 which associates the output circuit of the amplifier with the line section L Similarly the attenuation equalizer E is associated with the transformer 5' between the amplifier A andthe line section L Here again the efl'ect of the variable impedance of the equalizer upon the terminat ing two-wire line is reduced by reason of the fact that it is separated therefrom by means of a section of the line making up the four-wire link. A further modification is shown in Fig. 10 in which the attenu-ation equalizer E is inserted between the two halves of the secondary winding of Q the transformer 7 associated with the outgoing connection to the two-wire line I1 In a similar manner the attenuation equalizer E, is connected to the transformer 7 associated with the outgoing circuit to the ,,terminating two-wire line L,. This ar- ,rangement presents substantially the same advantages, so far as impedance relations are concerned, as the circuit shown in .Fig.- .6. In the four-w re system, it will be under- .stood that where-the four-wire link is'di vided into additional sections by means of additional repeater units that addition-ail. positions for thelocation of attenuationequalizers will be.,provided. Furthermore it will vbe understood that various combinations of the above described arrangements may be employed, if desired. a Other arrangements in addition to those already described might begsuggested, but the arrangements alreadydisclosedurge-,he:v

,llieved to suiiicientlvillustrate the prim ciples upon i, which this invention is based, the essential requirement being; that 5 the attenuation equalizersm associated with a transmission line and a repeater a1 .rangement that the losses introduced by the attenuation equalizer maybe made up. by Qthe repeater, the equalizer being preferably so arranged with regard to'theirepeater cir- -cuit'that the latterlwill reduce the reaction "between the attenuation equalizer and the h ltransmission line. It will be clear thattthe general rinciples herein disclosed may be 0 embodied in many other organizations eeann widely different from those illustrated, without departing from the spirit of the invention, as defined .in I the following claims.

What is claimed is:

1. In a transmission system, a transmission line the attenuation of which varies with frequency, a repeater system associated with said transmission line, said repeater systemincludin'g two amplifying transmission paths, one for transmitting in one direction, and the other for transmitting in the opposite direction, and a non-amplifying attenuation equalizing means associated with the repeater system and said transmission line, said equalizing means being so proportioned with reference to the line that the resultant attenuation of currents transmitted over the system will vary with frequency in a predetermined manner.

2. In a transmission system, a transmission line the attenuation of which varies with the frequency, a non-amplifying auxiliary system the attenuation ofvwhich varies with the frequency in a manner complemental to that of the transmission line so that the resultant transmission of the line and auxiliary system is substantially constant over a desired range of frequencies, and a repeater system associated with said lineand auxiliary system.

3. In a transmission system, a transmission line the attenuation of which varies with the frequency, a non-amplifying auxiliary system the attenuation of which varies with the frequency in-a manner complemental to that of the transmission line so that the resultant transmission of the line and auxiliary system substantially constant over a desired range of frequencies, and a repeater system associated with said line and auxiliary system, said repeater system" including two amplifying transmission paths, one for transmitting in one ,direction and the vother for transmittingin the-opposite direction. a

4-. In a transmission system, a,transmission line the attenuatiom ofr'which is greater lfor high frequencies than low frequencies, a non-amplifying auxiliary system the attesta p li eh. am -withttie qa y' in'a manner co inplemental to that' "of the transmission line so that the resultant. attenuation of the line and auxiliary "systenr is substantially constant overa desired range of frequencies, and a repeater system associated with saiddine and auxiliary system to make up the losses introduced by the auxiliary system.

' 5, In a transmission system, a transmission line the attenuation of which is greater for high frequencies than low frequencies, a non-amplifyin auxiliary'system the attenuation of whic varies with the frequency in a manner complemental to that of the ill! Inn

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transmission line so that the resultant attenuation of the line and auxiliary system is substantially constant over a desired range of frequencies, and a repeater system associated with said line and auxiliary system to make up the losses introduced by the auxiliary system, said repeater system including two amplifying transmission paths, one for transmitting in one direction and the other for transmitting in the opposite direction.

6. In a transmission system, a transmission line the attenuation of which varies with the frequency, a repeating system associated with said transmission line, said r'epeatingsystem comprising two amplifying transmission paths, one for transmitting in one direction and the other for transmitting in the opposite direction, and non-amplifying auxiliary systems whose attenuation varies with the frequency in a manner complemental to that of the line, said auxiliary systems bein included in the two transmission paths 0 the repeater system at points such that a portion of each path of considerable attenuation intervenes between the auxiliary system and the junction of the line andrepeater system.

7. In a transmission system, two geographically separated stations, terminating lines at said stations, a pair of transmission paths, interconnecting said stations, one

path being used for transmission in one direction and the other path for transmission direction, the attenuation over. a circuit including the two'terminating lines and one of said transmission paths varying with the frequency, non-amplifying auxiliary systems whose attenuation varies with the frequency 1n a manner complemental to that of said circuit, said auxiliary systems being inserted in said-transmission paths at intermediate points, and amplifying means in said paths.

8. In a transmission system, .a transmission line the attenuation of which varies with the frequency, non-amplifying means tenuation of the system-so that associated with said. line to equalize the attenuation of the system so that all frequencies within a desired range are transmitted with practically amplifying means to make up the loss intro.- duced by said first mentioned means.

9. In a transmission system, a transmission line the attenuation of which varies with the frequency, non-amplifying means associated with said line to equalize the atall frequencies within a desired range are transmitted with practically uniform attenuation, and amplifyingmeans to make up the loss 'introduced by said first mentioned means, and to increase the transmission efiiciency of the system.

10. In a transmission system, a transmission line the attenuation of which varies with frequency. in accordance with a known law, non-amplifying means associatedwith said line and having a characteristic such that the attenuation varies progremively with the frequency, tenuation of the combination varies with frequency in a different predetermined manner from that of the line above, and amplifying means to make up the losses introduced by said first mentioned means.

11. In a transmission system, a transmission line the attenuation of which vanes with frequency in accordance with a known law, a non-amplifying auxiliary system the attenuation of which is .predeterminable at different frequencies, said auxiliary system being so designed that the attenuation varies progressive when associated with the transmisslon llne the resultant attenuation varies with the frequency in accordance with a predetermined law, and amplifying means to make up the losses introduced by said auxiliary system.

In testimony whereof, I have signed my name to this specification this twenty-six day of June, 1918.

' OTTO B. 'BLACKWELL.

uniform attenuation, and

so that the resultant atly with the frequency, so that' 

